Large vessels, for example barges, have been and are being used in petroleum related activities such as, for example, pipe laying, well drilling, and assemblying offshore platforms. In general, these vessels should be maintained substantially stationary so that the work in which the vessel is engaged may proceed in an orderly and predictable fashion. As petroleum exploration ventures into more severe environments, for example the North Sea area, the problem of providing a stable and immobile vessel has increased dramatically. In these environments, waves on the order of ten to fifteen feet are not uncommon and to maintain the vessel within the specified limits of motion, for example a roll of less than two degrees and a pitch of less than one degree, is very difficult.
A related problem in adverse sea conditions relates to the relative motion and effectiveness of various smaller service craft which are typically found alongside the larger vessel. These craft have relatively high resonant frequencies and are highly responsive to wave action, much more than the larger vessels which they serve. In particular, waves reflected by the larger vessels, which will have a crest to trough amplitude of approximately twice the amplitude of the waves incident to the vessel, sometimes pose a threat to the service craft. Thus, reflected waves can and often do disturb and disrupt the normal activities of the service craft.
Various methods and structures have been developed to cope with the problems outlined above. To control motions of the vessel, many vessels use complex active apparatus to shift fluids from one portion of the vessel to another. Others use passive systems also involving moving fluids. Still further apparatus provide open tanks attached to the sides of the vessel which tend to reduce roll and reflected wave action. While many of these structures have tended to reduce the motions of the vessel, none has proven completely adequate from a practical point of view.
It is therefore an object of this invention to provide a passive structure attached to and forming a part of the sides of the vessel which further reduces the motions of the vessel and which also provides significantly reduced reflective wave action. It is a further object of the invention to provide apparatus to dampen the residual responses of the vessel and to maintain a desired mean water line for the vessel.
It is a further object of this invention to provide an apparatus which is simple in construction, which does not interfere with the normal sea going operations of the vessel, which may provide additional deck area, which does not interfere with docking of the vessel, and which enables the vessel to operate successfully in otherwise adverse conditions.